304 stainless steel industrial pipe has great differences in physical properties and chemical composition from structural steel, so the welding process of 304 stainless steel industrial pipe has its own characteristics.
Welding method and specification selection: 304 stainless steel industrial pipe can be welded by TIG, MIRG, PAW and SAW.
304 stainless steel industrial pipe welding, because of its low melting point, small thermal conductivity, large resistivity, the base metal and welding materials are easily heated and melted during welding, so the welding current used is relatively small, only about 80% of ordinary carbon steel. At the same time, narrow welds and narrow weld beads should be used to reduce the high temperature residence time, prevent carbide precipitation from affecting corrosion resistance, reduce weld shrinkage stress and reduce hot crack sensitivity.
Selection of 304 stainless steel industrial pipe welding materials
There are many varieties of austenitic stainless steel, the use environment is complex and changeable, and the choice of welding materials is a cautious and important work. The main basis for selecting welding materials for 304 stainless steel industrial pipes is:
- Select welding consumables according to the main chemical composition of stainless steel industrial pipe base material
- The composition of the welding consumables, especially the Cr and Ni alloying elements in the welding material is higher than that of the industrial pipe base material, for example, 18-8 welding using 19-9 welding materials, etc.
- Under the possible conditions, a welding material containing a small amount (4%-12%) of ferrite should be used to ensure good crack resistance of the weld.
- When the ferrite phase is not allowed or impossible in the weld of stainless steel industrial pipe, the welding consumables should use welding materials containing alloying elements such as Mo and Mn.
- C, S, P, Si, Nb of welding consumables should be as low as possible, especially C, S, P and other elements. Nb causes solidification cracks in pure austenitic welds, but there is a small amount of ferrite in the weld, which can effectively avoid
- Welding structures that need to be stabilized or stress-relieved after welding, usually using Nb-containing soldering materials.
Filling metals such as welding rods, welding wire, etc. should be selected according to the variety, specifications and matching welding processes of industrial pipes.
The 304 stainless steel industrial pipe has high thermal cracking sensitivity, which requires the weld metal composition to be roughly matched with the base material composition, and the ferrite content in the weld should be controlled. For weldments working at high temperatures for a long time, the ferrite content in the weld should be no more than 5%. Most of the 304 stainless steel tubes can be submerged arc welded. The welding wire should be made of low Si, low S, low P, and similar to the base metal. For austenitic stainless steel tubes with Cr and Ni content greater than 20%, in order to improve their crack resistance, high Mn (6%-8%) welding wire can be used. The flux should be alkaline or neutral flux to prevent welding to the weld. Increase Si. Austenitic stainless steel special flux increases Si, and can also transfer alloy to the weld to compensate for the burning of alloying elements, which can meet the requirements of weld performance and chemical composition. When submerged arc welding of 304 stainless steel industrial pipe, attention should be paid to selecting a thinner wire and a smaller welding line energy.
Source: China Stainless Steel Industrial Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)